Any of a wide variety of synthetic polymer s containing positively or negatively charged sites that can interact with or bind to an ion of opposite charge from a surrounding solution.
Light, porous solids in granules, beads, or sheets, they absorb the solution and swell as they attract the target ions; when exhausted, they are removed from use and regenerated by an inexpensive brine or carbonate solution. A solid support of styrene-divinylbenzene copolymer to which are attached sulfonic or carboxylic acid groups is often used to attract and exchange cation s (e.g., ions of hydrogen or metal s). Quaternary ammonium groups on the solid matrix are used to attract anion s (e.g., ions of chlorine ). Industrially, the resins are used to soften hard water , purify sugar , and concentrate valuable elements (gold, silver, uranium) from their ore s. In the laboratory they are used to separate and concentrate substances and sometimes as catalysts. Zeolite s are minerals with ion-exchange properties.